UPS systems come in a wide range of VA (volt amp) capacities to accommodate PCs and peripherals, such as modems and inkjet printers. You can easily calculate the VA capacity you need by adding the power draw of all the equipment you want connect to the UPS system. If the power draw of your equipment is expressed in amps, multiply that number by your nominal line voltage, which in North America is 120. If the power draw of your equipment is expressed in watts, multiply that number by 1.4.

Once you have calculated the total VA draw of your equipment, select a UPS system that is rated equal to or higher than that total. Standby UPS systems typically are rated 350VA, 500VA, 650VA, 800VA, 1000VA, and 1200VA, for example. Line Interactive UPS models will cover 700VA to 1400VA.

Our advice is to check the documentation of your computers and printers or contact the manufacturer to determine the exact power specifications and calculate the capacities needed for the UPS.